This invention relates to preserving and water-proofing of articles and materials such as wood, drywall, paper, other wood products, fabric, and concrete, to methods for producing hydrophobic materials and products, and particularly to the preparation and use of silane formulations for such purposes.
The utility of wood has been known for millenia, and the utility of wood products such as paper has been known for centuries. Wood has been as a weapon, a fuel source especially a material for the construction of items useful for society. Construction materials for the building of homes, boats, fences, telephone poles and furniture are but a few of the most common uses for wood.
However, throughout the history of man and his use of wood, this material has suffered from well known deficiencies, especially where wood products are used or stored in an outdoor environment.
Untreated wood and wood products typically begin to degrade after a brief period of exposure to sun, rain, seawater or potable water. Repeated wetting and drying cycles or freeze and thaw cycles can cause the wood to expand and contract to the point of destroying the wood product. Typically the wood will deform by swelling, warping and later cracking. Wood that contains more than 25% water will begin to rot. The formation of mold and mildew throughout the interior and exterior of the wood product will also take place and facilitate the degradation of the wood.
The exterior exposure of wood and wood products also renders the product vulnerable to insect damage. Termites, carpenter bees, ants and others species are known to degrade wood to the point where it is useless and turn the wood into dust. In some cases, the synergistic effects of both insects and weather work to quickly destroy wood. All of these degrading activities require the eventual repair and/or replacement of said wood products.
As a consequence, wood products, while ubiquitous and highly useful, generally have a limited lifetime, in some circumstances so limited as to exclude wood as a viable material of construction, paper as a medium for recording information, etc. Concrete products are also subject to deterioration from frequent and/or persistent infiltration of water and aqueous electrolytes under service conditions. As water penetrates, thermal expansion and contraction during the summer and ice expansion an contraction during winter commonly cause concrete to crack and fragment.
Thus, there has been a long-standing need for a preservation composition that meets the requirements of hydrophobicity and insecticidal properties, and that is economical, easy and safe to prepare and apply and possess an extended lifetime of service without losing potency.
Thompson U.S. Pat. No. 7,128,778 describes methods for treating wood or wood products comprising application of formulations containing boron, methyltrichlorosilane and an organic solvent such as tetrahydrofuran or a lower alkane. The process renders the treated wood products fire-resistant, water-resistant and wood consuming insect-resistant. Similar and related formulations and methods are described in Neal et al. U.S. Pat. No. 7,192,470, Thompson U.S. Pat. No. 7,267,714, and Thompson U.S. Pat. No. 7,300,502. Various related applications remain pending, including US 20090252873, US 20080047460, US 20080047467, US 20090053545, US 20090214688, US 20090261297, US 20070107630 and US 20080014110.
Kelsoe U.S. Pat. No. 6,902,767 describes treatment of wood with formulations comprising halosilanes, hydroxysilanes and alkoxysilanes in a water-miscible organic solvent. Water can optionally be present in very minor proportions, but is preferably excluded from the formulations. Specific silanes used in the Kelsoe formulations include methyltrichlorosilane. The formulations can also include boron compounds. The drawings depict structures that Kelsoe believe to be formed by reaction of the silane, the boron compound, or both with cellulose of the wood or wood product. Where the formulation contains a hydroxy or alkoxysilane, it preferably also contains a mineral acid which catalyzes reaction of the silane compound with cellulose.
Although the Thompson '778 formulations impart desirable properties to wood, paper, or other wood products, and the Kelsoe formulations are said to achieve such effect also, there are well known disadvantages to the use of organic solvents. Organic solvents generally, including the lower alkanes of Thompson '778, acetone, alcohols and acetonitrile of Kelsoe '767, and tetrahydrofuran favored in both references, are highly volatile, flammable, and toxic. The preparation and use of organic solvents requires arrangements for ventilation, fire suppression, and preferably solvent recovery. If the solvents are not recovered they constitute emissions that create toxicity issues, may be subject to regulatory restrictions, and constitute greenhouse gases that potentially aggravate the problem of preventing atmospheric warming or other climate effects.
Prior to the present invention, however, it has been considered essential to use non-aqueous solvents, and in particular organic solvents, for halogenated silanes because the halogenated silanes are readily hydrolyzed by contact with water with release of hydrogen halide gas such as HCl. In fact, the trihalosilanes that are used in the formulations and methods of the Thompson and Neal patents react violently when contacted with water. They can readily ignite under these conditions and the resulting conflagration may be difficult to extinguish.
Thus, prior to the present invention, it has been considered necessary to accept the disadvantages of toxicity, flammability, solvent recovery, waste disposal, and expense associated with the use of organic solvents for halosilane, hydroxysilane and alkoxysilane wood treatment formulations.
Processes are known for producing hydrophobic concrete. For example, Johansson et al. U.S. Pat. No. 6,833,091 describes a method for stabilizing gravel, sand, crushed stone, rock and concrete structures which have cracks by injecting a pumpable low viscous aqueous aerated concrete with a pore volume≧20% into the cracks. If hydrophobic aerated concrete is desired, the hydrophobicity can be increased by adding rosin in an amount of 0.1-2.5 parts by weight per 100 parts by weight of cement. The presence of an anionic surfactant comprising aryl disulphonates and/or a colophonium or phenol-modified colophonium resin further contribute to the hydrophobicity of the aerated concrete.
Cuthbert U.S. Pat. No. 5,073,195 describes treatment of wood, masonry, paper, textiles and a variety of other substrates with aqueous solutions comprising combinations of an alkyltrimethoxysilane such as methyltrimethoxysilane or isopropyltrimethoxysilane and a water-soluble coupling agent comprising an aminoalkylsilane such as N-(2-aminoethyl)-3-aminopropyltrimethoxysilane or a quaternary ammonium functional silane. Methyltrimethoxy-silane is listed as a coupling agent but all examples and claims call for an aminoalkylalkoxysilane or quaternary salt. The mole ratio of alkyltrialkoxysilane to coupling agent is between about 0.5:1 and about 3.0:1, preferably 1.5:1 to about 2.0:1 in order to provide stable solutions. Aqueous solutions outside these ranges of ratios are said to form gels. Cuthbert describes only topical treatment of wood or masonry products.
DePasquale et al. U.S. Reissue Pat. 33,759 describes an aqueous emulsion for imparting water repellency to concrete and other porous masonry surfaces. the emulsion may comprise an alkyltrialkoxysilane such as octyltriethoxysilane and an emulsifier comprising a nonionic surfactant. The exemplary formulations comprise octyltriethoxysilane and either a sorbitan fatty acid ester or polyoxyethylene sorbitan fatty acid ester. A lengthy list of alternative silane reagents includes methyltrimethoxysilane, tridimethylaminosilane, octyltrichlorosilane, etc. One example contains octyltriethoxysilane and 0.5 wt. % acetic acid, while another contains octyltriethoxysilane and 1.0 wt. % triethylamine. The surfactants are said to act as inhibitors of hydrolysis in the absence of an acid or alkaline medium but in the acid or alkaline medium of the masonry, e.g., concrete, or the like, hydrolysis is said to occur readily with the desired chemical bonding with the substrate.
Thomas U.S. Pat. No. 5,776,245 describes preparation of a hydrophobic gypsum product in which a hydrophobic additive is dispersed in an aqueous gypsum mixture. The additive comprises a polysiloxane and a silane of the general formula (RO)2SiRR′ or (RO)3SiR′ in which R′ is preferably an amino, amino-loweralkylene-amino or dialkylenetriamino group. Various prior art references describing formulations comprising a coupling reagent are discussed in the background of the Thomas '245 patent.
Thomas U.S. Pat. No. 5,855,667 is similar to the Thomas '245 patent but does not require a polysiloxane. As in the '245 patent, a preferred combination is methyltrimethoxysilane and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane. The ratio of the first silane, e.g., methyltrimethoxysilane, to the second silane, i.e., the aminoalkylsilane, is said to range preferably from 1:1 to 9:1, while the exemplified range is from 2.33: to 4:1. The reported results indicate significantly higher water absorption by the gypsum product produced at a 4:1 ratio as compared to 2.33:1. Three comparative examples use methyltrimethoxysilane alone, with relatively high water absorption results. The formulations of Thomas '667 do not include an acid catalyst.
Göbel U.S. Pat. No. 6,139,622 is directed to a process for the production of a homogenously waterproofed concrete (integrally water-proofed concrete) in which an aqueous hydroylzable emulsion containing organosilicon compounds is added before curing to the fresh concrete mix prepared from water. The organosilicon compound can be an alkyltrialkoxysilane, preferably n-octyltriethoxysilane and hexadecyltriethoxysilane. The working examples combine these two alkyltrialkoxysilanes with a silane surfactant. In a preferred embodiment, and in particular also in the case of emulsions containing short-chain silanes, for example containing C3 and C4 alkylene groups, an acidic catalyst is added shortly before use which is capable of breaking the Si—O bonds, but not the Si—C bonds, in the claimed alkoxysilanes, in order to improve the effectiveness of the silanes on neutral, weakly acidic or alkaline, in particular problematic, surfaces.
Japanese published application 2002-013902 describes preparation of silane incorporated paper by adding a silane compound to the pulp slurry. The silane-incorporated paper is composed of an aggregate of vegetable fibers and contains a silane compound in a proportion of ≧2 wt %, preferably 5-20 wt. % with respect to SiO2. The use of an amine coupling agent is preferred. An epoxy coupling agent may also be used. The exemplary disclosure uses a combination of N-(2-aminoethyl)-3-aminopropyl-trimethoxysilane and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane. The aqueous medium for the alkoxysilanes contains a significant concentration of isopropanol.